In many modern electronics applications, it is desirable to convert an analog signal to a digital value. For example, in a radio frequency (RF) transceiver, a received analog RF signal may be demodulated to an analog baseband signal which is then converted to a digital baseband signal for subsequent digital signal processing.
Many electrical systems utilize analog-to-digital converters (ADCs) to convert an analog input signal to a digital output value. However, because of the finite nature of digital representation, quantization error (which is the difference between the actual analog value and quantized digital value due to rounding or truncation) is an imperfection inherent to the analog-to-digital conversion. If the voltage resolution of the ADC is large relative to the input signal voltage, the quantization error increases and degrades the signal-to-noise ratio (SNR) of the ADC. As a result, most ADCs are designed with a voltage resolution and/or voltage range tailored for a particular input signal range (e.g., amplitude or voltage swing) to minimize the quantization error of the ADC. However, different communications standards (e.g., wideband code division multiple access (WCDMA), long term evolution (LTE), Global System for Mobile communications (GSM), and the like) often specify analog signals with different signal ranges. Most ADCs are designed to accommodate a particular communications standard, and as a result, the performance characteristics of a particular ADC may be inadequate for use with a different communications standard. For example, the voltage resolution and/or voltage range may be too large or too small for a different communications standard, thereby resulting in unacceptably high SNR for the ADC.
Rather than utilizing separate ADCs for each communications standard, some prior art systems utilize variable gain amplifiers, attenuators, and other techniques to adjust the analog input signal to a voltage level that is more compatible with voltage resolution and/or voltage range of the ADC. These systems add components to the ADC architecture, thereby increasing the size and/or current requirements for the ADC, and in some situations, negatively impact the noise performance (e.g., the SNR) of the ADC.